The present disclosure relates to systems and methods that provide optical signals over a cable transmission network.
Cable television (CATV) networks have evolved significantly since first being deployed as relatively simple systems that delivered video channels one-way from a content provider. These early systems included transmitters that split a number of CATV channels among several frequency bands, each of approximately 6 MHz, time multiplexed those signals, and sent them to subscribers as an electrical signal through a network of coaxial transmission lines to cable modems or set-top boxes in subscribers homes. Early evolution of such systems permitted limited return communication from the subscribers back to the content provider either through telephone lines or a dedicated, small, low-frequency signal propagated onto the coaxial network.
Modern CATV networks differ from these early networks in several material respects. First, given the growth of content provided to customers over increasing distances, much of the coaxial transmission path has been replaced by fiber-optic lines, although the trunk lines and feeder cables to customer homes remain coaxial, and much of the content delivered to the provider for transmission is by an analog electrical signal that the provider must then convert to an optical signal for propagation onto the coaxial transmission grid. Nodes, located closer to the subscribers receive the optical signals from the transmitter and convert them to the electrical signals for delivery to the subscribers through the coaxial lines to the subscribers' homes. Such a network is commonly referred to as a Hybrid Fiber-Coax (HFC) system.
Second, in addition to delivering television content, modern HFC systems also deliver additional content including Video-on Demand (VOD) and data services such as Internet access. These services require not only a high-capacity transmission path in the direction from the content provider to the subscriber but require a high capacity transmission path in the direction from the subscriber back to the content provider. Additional quality is needed both for new high definition broadcast channels and for the narrowcast video and data services. The original HFC network has been successfully updated to deliver new services, but the pressure of HD, VOD, and data service requires further advances, thus there is significant continuing pressure to increase the quality of data sent over a HFC network.